The group B Coxsackievirus, which are the principal cause of viral heart muscle disease in the human, are to be studied in a primate species as to the relative contributions of the virus, and the respective humoral and cellular immune response to the pathogenesis of acute and chronic myocarditis. Squirrel monkeys (Saimiri sciureus) will be inoculated with Coxsackievirus B-4. Acute and chronic myocardial damage will be determined histologically and related to the presence of virus measured by virus titration and by localization of virus in heart muscle cells examined by immunofluorescence and electron microscopy. Coxsackievirus induced humoral immune response will be investigated relative to antibody reacting with virus, with virus infected cells, with de novo induced viral and non-viral cardiac antigens and by th demonstration of circulating immune complexes. The cellular immune response will be examined in terms of the activity of specific members of the lymphocyte population to react with the virus and to virus infected cells. Immunosuppression induced by treatment with antithymocyte serum or by administration cortisone prior to virus inoculation will be used in an attempt to establish a viral induced chronic myocarditis. Virus related humoral and cellular immune responses will be followed during a six month period of observation. This data will be correlated ultimately with histologic examination of monkeys in the respective treatment groups at the time of termination of the experiment.